Electronic switching power converters accept electric power from a source and convert it into a form suitable for use by a load. As used herein, a power converter refers to devices that convert electric power received from a source (AC or DC) for delivery to a load, providing some of the following functions: voltage transformation (step-up or step-down), regulation (current, voltage, or power), and galvanic isolation. Examples of switching power converters include DC-DC converters, switching regulators, and DC Transformers such as Voltage Transformation Modules.
As used herein, the power density of a power converter refers to the full rated output power of the power converter divided by the volume occupied by the converter. Trends in contemporary power conversion have resulted in dramatic increases in power density of marketable power converters. Prior to 1984, power densities were typically below 10 Watts-per-cubic-inch. In contrast, power densities greater than 500 Watts-per-cubic-inch have become possible today. A very high density, galvanically isolated, point of load DC-to-DC transformer, called a Sine Amplitude Converter “VTM” is described in Vinciarelli, Factorized Power Architecture With Point of Load Sine Amplitude Converters, U.S. Pat. No. 6,930,893, issued Aug. 16, 2005 (the “SAC Patent”).
As used herein, the current density of a power converter refers to the full rated output current of the converter divided by the board area occupied by the converter. Current density specifications are trending up in some microprocessor (referred to herein as “CPU's”) applications. For example, some microprocessors are approaching current specifications up to about 100 Amperes or more. Moreover, the dynamic load requirements call for the power converter that supplies such currents to be in close proximity to the CPU. Commercially available solutions are characterized by a current density of less than 10 Amps-per-square inch. Sine Amplitude Converter VTMs, such as those described in the SAC Patent, are capable of providing the low voltage requirements of future microprocessors with current densities exceeding 50 Amps-per-square inch. They utilize a multi-layer circuit board assembly including transformer core structures protruding from both sides of the circuit board. Output currents in excess of 50 Amperes need to be carried from the converter's PCB, at one elevation, and then to the CPU board at a different elevation. The interconnections associated with these elevation changes call for low resistance and low inductance consistent with the current slew rate requirements of a highly dynamic load.
In general, power converters dissipate heat in operation. Increases in power density can complicate thermal management, particularly where the increase in power density exceeds the corresponding increase in efficiency, the net effect of which is a net increase in heat density. Thus, advancements in power conversion technology may often present significant challenges in terms of thermal management technology. These challenges impose constraints on the packaging architecture used to house the converter and its input and output terminals. For example, the power converter package must exhibit low thermal resistance between its internal hot spots, particularly its semiconductor junctions, and external heat sinks. Depending on the specific thermal environment surrounding the power converter, it is desirable to remove heat from the converter package through its case and/or terminals. Low junction-to-case and junction-to-terminal thermal resistances help to keep internal temperature rises acceptable. However, a good thermal interface should not interfere with the need for flexible mounting of the power converter package. Furthermore, a solution should provide for mechanical tolerances of the converter package and of the system with which the converter is coupled.
With available space for components on printed circuit boards at a premium, a power supply on the board can complicate signal routing to a high-pin count component, such as a CPU. In some bulk power solutions, the bulk power supplies are located at a distance from the load to avoid dissipating additional heat near the processor. This allows for a greater ease in keeping components on the board together without occupying significant space around the CPU or generating heat concerns in close proximity to the load components.
A power conversion apparatus, in which a power converter is mounted in an aperture in a circuit board, and in which a compliant connection scheme along the sides of the power converter allows for variation of the extension of the power converter within the aperture, is described in Vinciarelli et al, Mounting Electronic Components on Circuit Boards, U.S. Pat. No. 6,623,281, issued Sep. 23, 2003 (assigned to the same assignee as this application and incorporated by reference). A power conversion apparatus, in which a power converter is mounted in an aperture in a circuit board, and in which at least four sides of the power converter, including the two sides which lie entirely above and below the surfaces of the circuit board, are covered with heat sinks to aid in the removal of heat from the power converter, is described in Vinciarelli et al, Power Converter Packaging, U.S. Pat. No. 6,434,005, issued on Aug. 13, 2002 (assigned to the same assignee as this application and incorporated by reference).
Techniques for over molding electronic components on one side of a substrate are known. In one example, electronic devices mounted on one side of a printed circuit board assembly are over-molded with encapsulant and the other side of the printed circuit board assembly, which is not over-molded, comprises a ball grid or a land grid array of electrical contacts. The package architecture sometimes referred to as “System In a Package” (SIP) provides some of the electrical, mechanical and thermal management characteristics required of high power density and high current density converters. However, the SIP architecture is incompatible with two-sided circuit board assembly including transformer core structures protruding from both sides of the circuit board. Furthermore, the SIP package provides limited mechanical and thermal management flexibility.
Intel Corporation, Santa Clara, Calif., USA, manufactures microprocessors which are packaged in a package, called a Micro-FCPGA package, which comprises a component over molded on one side of a substrate and a pin-grid-array and exposed capacitors on the other side of a substrate.
Saxelby, Jr., et al, Circuit Encapsulation Process, U.S. Pat. No. 5,728,600, issued Mar. 17, 1998, and Saxelby, Jr., et al, Circuit Encapsulation, U.S. Pat. No. 6,403,009, issued Jun. 11, 2002 (both assigned to the same assignee as this application and both are incorporated herein in their entirety by reference) describe ways of over-molding both sides of a printed circuit board assembly while leaving opposing regions on both sides of the printed circuit board free of encapsulant. This is useful for exposing a row of contacts that extend along an edge of the printed circuit board on both sides of the board.